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Right on schedule, Dipper appeared in the space next to Mabel.
“Hey bro-bro!” she said, grinning. “You made it! How’d the summons go?”
“It was okay.” He was busy dusting himself off, paying attention to some strange white chunks that were stuck to his outfit. When he looked up, Mabel saw three bloody lines cut into his cheek, and they twisted up when he returned her smile. “I’m still getting used to the whole ‘negotiation’ thing. But on the bright side, the power that I got from the deal should be enough to keep me physical for an hour or two.”
Mabel squealed and did a little dance. “Awesome! Nothing can stop the Mystery Twins from taking on their first Halloween as technically teens! Especially since I’m Ducktective! If there’s a candy thief to be found, I’ll track them down and then ka-pow them right in the noodle!”
Dipper snorted. “Could Ducktective even punch anyone? I mean he is a duck.”
“Yeah? Well... I’ve got this big magnifying glass. I bet it’d leave a nasty mark if I threw it at their head!” Mabel crossed her arms and looked her brother up and down. “Besides, I don’t see you wearing a costume. Where’s your holiday spirit? Cmon, we gotta play the twins angle if we want to get as much candy as possible!”
“Oh, I’ve got a costume!” Dipper replied, with visible excitement. He stuck his arms out in a T-pose and began to spin. For a minute, he was only a blur, and when he slowed down again he was in a bright red trench coat with a matching fedora, and long black boots. He put his hands on his hips in a triumphant pose, and beamed at Mabel expectantly.
She frowned, nonplussed. “Are you, like, evil Inspector Gadget? I don’t think that works with our theme.”
“Noooooooo!” Dipper cried, throwing his arms up. “I’m Carmen Sandiego! Remember that show from when we were kids? She would go around the world stealing treasure and everyone was always trying to track her down and she was so cool??” He glared at her with the most spectacular scowl on his face, and a waft of steam rose out of his hat.
"Oh yeah!” She giggled and bopped him on the head -- recoiling a bit when she found him to be scalding hot to the touch, but even that proved to be hilarious to her. “It seemed like no one could crack the case of the missing Faberge eggs, until the legendary DUCKTECTIVE tracked down Carmen Sandiego and brought her to justice!”
Dipper’s mouth stretched wide and he bared his teeth at her. “You’ll never bring me to justice! I stole these fangs from the most well-funded museums in Europe, and I’m not afraid to use them!”
The twins stared at each other, and then broke into a fit of laughter. They looped their arms around one another and marched toward their first house, talking about their days and swapping Halloween jokes the whole way.
“You know, this is probably the last year we can do this,” Dipper said eventually.
Mabel’s grin faltered, and she cut off in the middle of singing Spooky Scary Skeletons. “Oh, come on bro-bro, I don’t wanna hear any of this we’re getting too old stuff. Halloween is a state of mind, it’s a way of life, it’s -”
“No no no,” he broke in. “That’s not it. I mean, we are getting older, but I know there’s no force in the universe that can stop you from going trick-or-treating. Me, on the other hand...”
“You?” Mabel stopped walking, nearly causing Dipper to topple over. “Whaddaya mean?”
He sighed, and looked up at the sky. “Well. I got summoned twice today. And I only get summoned like once a month, so I don’t think it’s a coincidence that two different people chose today to invite a demon into their home.”
Dipper’s grip on her hand tightened, and she felt the prick of claws pressing gently into her skin. “I think the only reason I don’t get summoned very often right now is because I’m kind of unknown. But as time goes on, that’s going to change, and that means more people are going to want to summon me, and that means more people are going to want to summon me on Halloween.”
“Oh,” Mabel said.
The pressure on her hand eased up as he withdrew into his coat. Mabel sniffed. Held her hand up and examined the little lines he’d left behind. She looked past it to where her brother was staring forlornly into the night, as if it were moments away from swallowing him up.
“Well, I’ll just have to summon you myself, then.”
“What?” he exclaimed, doing a double-take.
Mabel took his arm again and elbowed him in the side. “I’ll just summon you myself! If random losers in their parents’ basement can do it, why can’t I? A summons from a sister has gotta be better than that, right?”
Dipper’s lip wobbled. “Technically, but it’s complicated...”
“Well, if that doesn’t work, we’ll figure something out, alright?” Mabel grabbed her magnifying glass and held it up like a staff. “I won’t give up on this case! I bet I can ask Grunkle Ford if there’s anything in his research about demon summoning. And there’s always Summerween! No one outside of Gravity Falls has ever even heard of it so I don’t think you have to worry about being summoned then!”
“That is true,” he admitted. “But...”
She tugged on his arm and pointed up the driveway they were standing in front of. “So for now, let’s just have fun, okay? I want to see how much candy I can eat before I see into the future!”
Dipper stuck his tongue out at her. “Alright, but I’m not cleaning up after you. Not even if you pay me,” (he saw her open her mouth and he sped up) “not even if you pay me with candy.”
Mabel shrugged. “We’ll see about that, Mr. Dreambender.”
She knocked on the door, and an old woman stepped out of the house holding a bag of candy.
“Well, hello dears,” she said. “My, what lovely costumes! Am I correct in guessing that you’re Sherlock Holmes?”
“Ducktective!” Mabel replied. “Quack quack!”
“Oh, of course! And, hmm...” She bent down to get a closer look at Dipper -- observing his fancy outfit, black-and-yellow eyes, pointy ears -- and he gave her a toothy smile. “I bet you’re some kind of gay vampire, right?”
Dipper’s face went as red as his costume, as every muscle in his body tensed up at once and steam began to rise from his head again. “I’m- no- I’M- !”
Mabel cackled, watching her brother crumple to the floor dramatically. “Wow, congrats, Mrs. Jenkle! I think that’s the scariest thing he’s heard all day! Happy Halloween, bro-bro!”